The present invention relates to a method of controlling the operation of a thermoelectric power station and, more particularly, to a method which permits a quick start up of the plant while keeping the thermal stress occurring in the thick-walled part of the plant below a predetermined allowable level.
In recent years, thermoelectric power plants are used for medium levels of load to work in hamonization with nuclear power plants. In these thermoelectric power plants, the operation of the steam generating equipment, as well as the operation of the turbines, is controlled in accordance with plant operating parameters which are obtained from given patterns of start up and operation of the plant. These thermoelectric power plants are required also to respond to the demands for quick start up and stop, as well as demand for drastic change of the load level. It is, therefore, quite important to precisely determine the thermal stresses occurring in the thick-walled parts of the steam generating equipment and turbine, and to control the start up and stopping of the plant, as well as the running of the same, in such a manner as to minimize the consumption of the lives of these parts. When the plant is started up, a specifically large thermal stress occurs in the tube header of the secondary superheater of the steam generating equipment, as well as in the rotor surface and the bore of the turbine rotor adjacent to the labyrinth packing of the first stage.
It is quite difficult to determine the thermal stressed in these parts or to actually measure the temperature distributions around these parts for giving bases to the calculation of the thermal stresses. The measurement of temperature is difficult particularly for the rotor which rotates at a high speed during the operation. In addition, since the condition of the steam varies at every moments, it is almost impossible to accurately determine the thermal stress actually occurring in these parts of the plant. For these reasons, hitherto, it has been a common measure to determine the operation parameters including the starting schedule in accordance with the steam condition before the start up. In this method, however, a large margin is involved accounting for the deviation of the actual steam condition from the planned one. Consequently, unnecessarily long time was taken for the plant to be started up.
In addition, since the control of the steam temperature, which is the factor ruling the thermal stress, suffers from a considerable time lag, it has been materially impossible to conduct a feed-forward control on the basis of the thermal stress.
Under these circumstances, a method has been proposed recently in the specification of U.S. Pat. No. 4,228,359, in which the thermal stresses occurring in various parts of the turbine rotor are estimated and the operation parameters such as acceleration rate, load changing rate and so forth are corrected in view of the estimated thermal stresses. In these methods, the control is made on the basis of the condition of steam generated in the steam generating equipment, and the control of the operation of the plant is made independently of the control of the steam condition in the steam generating equipment. Consequently, the harminization between plants is often failed due to, for instance, a stop of the temperature rise, resulting in an impractically long time for the starting up of the plant.
On the other hand, no practical proposal has been made up to now as to a method in which the boiler is controlled on the basis of thermal stresses estimated to be occurring in the boiler.